Aqueous dispersion containing a complex of poly(3,4-dialkoxythiophene) and a polyanion and method for producing the same

ABSTRACT

An aqueous dispersion used for producing a conductive film is provided. The dispersion contains a complex of poly(3,4-dialkoxythiophene) and a polyanion, and is produced by polymerizing 3,4-dialkoxythiophene in an aqueous solvent in the presence of the polyanion by using peroxodisulfuric acid as an oxidizing agent or by using an oxidizing agent and an acid that is employed so as to lower pH of the reaction mixture.

CROSS REFERENCE TO RELATED PATENT APPLICATION

The present patent application claims the right of priority under 35U.S.C. §119 (a)-(d) of Japanese Patent Application No. 2002-217571,filed Jul. 26, 2002.

FIELD OF THE INVENTION

The present invention relates to an aqueous dispersion containing acomplex of poly(3,4-dialkoxythiophene) and a polyanion and a method forproducing the same. The present invention also relates to a coatingcomposition containing the water dispersion and a substrate having aconductive transparent film obtained by applying the coating compositionon a surface to a substrate.

BACKGROUND OF THE INVENTION

Conductive transparent films are employed for coating transparentelectrodes of liquid crystal displays, electroluminescence displays,plasma displays, electrochromic displays, solar cells, touch panels andthe like, and for coating substrates such as those made ofelectromagnetic shielding material. The most widely employed conductivetransparent film is a vapor deposited film made of indium-doped tinoxide (i.e., ITO). However, the formation of ITO film by a vapordeposition process has problems such as the necessity of a hightemperature for film formation and high cost for film formation. ITOfilm can be formed by a coating method. However, the film formation bythis method requires a high temperature, the conductivity of the filmdepends on the degree of dispersion of ITO, and the haze value of thefilm is not always low. Furthermore, for an inorganic oxide film such asan ITO film, cracks tend to be generated by the bending of thesubstrate, so that the conductivity may be reduced.

On the other hand, a conductive transparent film made of conductivepolymer that can be prepared at a low temperature and a low cost hasbeen proposed as a conductive transparent film made of an organicmaterial. As for the conductive polymer that can be used for such afilm, Japanese Patent Publication No. JP 2636968 discloses a complex ofpoly(3,4-dialkoxythiophene) and a polyanion and a method for producingthe complex. This complex has good water dispersibility. A thin filmproduced by applying a coating, composition containing an aqueousdispersion of the complex to a substrate has a sufficient antistaticfunction, but insufficient transparency and conductivity.

Japanese Laid-Open Patent Publication No. JP 8-48858 describes that athin film produced by applying a coating composition to a substrate hasan improved conductivity, wherein the coating composition is obtained byadding a compound that is selected from the group consisting of acompound having two or more hydroxyl groups, a compound having an amidegroup, and a compound having a lactam group to an aqueous dispersioncontaining a complex of poly(3,4-dialkoxythiophene) and a polyaniondescribed in Japanese Patent Publication No. JP 2636968. JapaneseLaid-Open Patent Publication No. JP 2000-153229 describes that a thinfilm produced by applying a coating composition containing a non-protoncompound having a dielectric constant of ∈≧15 to a substrate and dryingthe resultant substrate at a temperature less than 100° C. has animproved conductivity.

The properties of all the coatings compositions described in thesepublications are improved by adding a specific compound to the waterdispersion containing a complex of poly(3,4-dialkoxythiophene) and apolyanion described in Japanese Patent Publication No. JP 2636968, andthe conductivities thereof are comparatively improved. However, thewater dispersion containing the complex (i.e., a conductive polymer) isthe same, so that the transparency and the conductivity of the resultantfilm obtained from the water dispersion are not necessarily sufficient.

SUMMARY OF THE INVENTION

The present invention is directed to solve the above-described problems,and the objective thereof is to develop an aqueous dispersion containinga conductive polymer that can be formed into a conductive thin filmhaving excellent transparency and conductivity and a coating compositioncontaining the water dispersion.

The inventors of the present invention found out that an aqueousdispersion containing a conductive polymer having excellent transparencyand conductivity can be obtained by using peroxodisulfuric acid as anoxidizing agent or using an arbitrary oxidizing agent in combinationwith an acid that is used for lowering the pH in polymerizing(3,4-dialkoxythiophene) in the presence of a polyanion, as a result ofin-depth research to solve the problems, and thus achieved the presentinvention.

The present invention provides a method for producing an aqueousdispersion containing a complex of poly(3,4-dialkoxythiophene) and apolyanion comprising: polymerizing 3,4-dialkoxythiophene represented byformula (1):

wherein R¹ and R² are independently hydrogen or a C₁₋₄-alkyl group, ortogether form a C₁₋₄-alkylene group which may optionally be substituted,wherein the polymerization is performed in the presence of the polyanionby using peroxodisulfuric acid as an oxidizing agent in an aqueoussolvent.

The present invention provides a method for producing an aqueousdispersion containing a complex of poly(3,4-dialkoxythiophene) and apolyanion comprising: chemically oxidatively polymerizing3,4-dialkoxythiophene represented by formula (1):

wherein R¹ and R² are independently hydrogen or a C₁₋₄-alkyl group, ortogether form a C₁₋₄-alkylene group which may optionally be substituted,wherein the polymerization is performed in the presence of the polyanionby using an oxidizing agent in an aqueous solvent, in which an acidselected from the group of water-soluble inorganic acids andwater-soluble organic acids is added so as to lower pH of the resultantreaction mixture.

The present invention provides a method for producing an aqueousdispersion containing a complex of poly(3,4-dialkoxythiophene) and apolyanion comprising: polymerizing 3,4-dialkoxythiophene represented bythe formula (1):

wherein R¹ and R² are independently hydrogen or a C₁₋₄-alkyl group, ortogether form a C₁₋₄-alkylene group which may optionally be substituted,wherein the polymerization is performed in the presence of the polyanionby using peroxodisulfuric acid as an oxidizing agent in an aqueoussolvent, in which an acid selected from the group of water-solubleinorganic acids and water-soluble organic acids is added so as to lowerpH of the resultant reaction mixture.

The present invention also provides an aqueous dispersion containing acomplex of poly(3,4-dialkoxythiophene) and a polyanion obtained by theabove-described method.

The present invention further provides a coating composition comprisingan aqueous dispersion containing a complex ofpoly(3,4-dialkoxythiophene) and a polyanion; and a compound selectedfrom the group consisting of water-soluble compounds having an amidegroup, water-soluble compounds having a hydroxyl group, water-solublesulfoxides, an water-soluble sulfones.

The present invention further provides a substrate having a conductivetransparent film produced by applying the above-mentioned coatingcomposition on a surface of a substrate an drying the resultantsubstrate.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the relationship between the total lighttransmission and the surface resistivity of a coated substrate obtainedby the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail.

The method for producing an aqueous dispersion containing a complex ofpoly(3,4-dialkoxythiophene) an a polyanion of the present inventionincludes polymerizing 3,4-dialkoxythiophene represented by formula (1):

wherein R¹ and R² are independently hydrogen or a C₁₋₄-alkyl group, ortogether form a C₁₋₄-alkylene group which may optionally be substituted,wherein the polymerization is performed in the presence of the polyanionby using peroxodisulfuric acid as an oxidizing agent in an aqueoussolvent, or using an oxidizing agent in an aqueous solvent, in which anacid selected from the group of water soluble inorganic acids andwater-soluble organic acids is added so as to lower pH of the resultantreaction mixture.

In 3,4-dialkoxythiophene, preferable examples of the C₁₋₄-alkyl groupsrepresented by R¹ and R² include a methyl group, an ethyl group, and ann-propyl group. Examples of the C₁₋₄-alkylene group formed by R¹ and R²together include a 1,2-alkylene group and a 1,3-alkylene group,preferably a methylene group, a 1,2-ethylene group, and a 1,3-propylenegroup. Among these, the 1,2-ethylene group is particularly preferable.The C₁₋₄-alkylene group may optionally be substituted, and examples ofthe substitute include a C₁₋₁₂-alkyl group and a phenyl group. Examplesof a substituted C₁₋₄-alkylene group include a 1,2-cyclohexylene groupand a 2,3-butylene group. The 1,2-alkylene group that can be formed byR¹ and R² together an that may be substituted with a C₁₋₁₂-alkyl groupis a typical example of the alkylene groups. This 1,2-alkylene group canbe derived from 1,2-dibromoalkanes that can be obtained by brominationof an α-olefin such as ethene, propene, hexene, octene, dodecene, orstyrene.

Examples of the polyanion used in the above-described method include apolycarboxylic acid such as polyacrylic acid, polymethacrylic acid andpolymaleic acid, and a polysulfonic acid such as polystyrene sulfonicacid, and polyvinyl sulfonic acid. Among these, polystyrene sulfonicacid is particularly preferable. The polycarboxylic acid may be acopolymer of vinyl carboxylic acid and another polymerizable monomer,and the polysulfonic acids may be a copolymer of vinyl sulfonic acid andanother polymerizable monomer. Examples of the polymerizable monomerinclude acrylates and styrene. The number average molecular weight ofthe polyanion is preferably in the range from 1 000 to 2 000 000, morepreferably 2 000 to 500 000, and most preferably 10 000 to 200 000. Theamount of the polyanion used is preferably 50 to 3 000 parts by weight,more preferably 100 to 1 000 parts by weight, and most preferably 150 to500 parts by weight with respect to 100 parts by weight of thethiophene.

The solvent used in the above-described method is an aqueous solvent, anwater is particularly preferable. Alternatively, water containing awater-miscible solvent such as alcohols, (e.g., methanol, ethanol,2-propanol and 1-propanol), acetone, and acetonitrile can be used:

In the method of the present invention, examples of the oxidizing agentused in a polymerization reaction of 3,4-dialkoxythiophene include, butare not limited to, peroxodisulfuric acid, sodium peroxodisulfate,potassium peroxodisulfate, ammonium peroxodisulfate, inorganic salts offerric oxide, such as iron(III) salts of inorganic acids, organic saltsof ferric oxide, such as iron(III) salts of organic acids, hydrogenperoxide, potassium permanganate, potassium dichromate, perboric acidalkaline salts, and copper salts. Among these, peroxodisulfuric acid,sodium peroxodisulfate, potassium peroxodisulfate and ammoniumperoxodisulfate are most preferable. The amount of the oxidizing agentused is preferably 1 to 5 equivalents, and more preferably 2 to 4equivalents, with respect to one mole of the thiophene.

In the method of the present invention, it is preferable that the pH ofthe reaction mixture during polymerization is low (preferably 1.5 orless). For this reason, when peroxodisulfuric acid is selected from theabove-listed oxidizing agents, simply adding it to the reaction systemwithout adjusting the pH is sufficient for preferable use. When otheroxidizing agents are selected, it is necessary to add an acid to adjustthe pH. The pH of the reaction mixture is preferably 1.5 or less, andmore preferably 1.0 or less.

As the acid, an acid selected from the group of water-soluble inorganicacids and water-soluble organic acids can be used. Examples of inorganicacids include hydrochloric acid, sulfuric acid, nitric acid andphosphoric acid. Examples of the organic acids include p-toluenesulfonicacid, benzenesulfonic acid, methanesulfonic acid, andtrifluoromethanesulfonic acid.

Furthermore, as the oxidizing agent, a catalytic amount of metal ions,such as iron, cobalt, nickel, molybdenum, and vanadium ions (compoundsthat can form such metal ions) can be added, if necessary.

The temperature of the reaction mixture during polymerization in themethod is 0 to 100° C., preferably 0 to 50° C., and more preferably 0 to30° C. for suppression of side reactions.

The polymerization reaction can be performed for 5 to 100 hours,depending on the type and the amount of the oxidizing agent, thepolymerization temperature, the pH of the reaction mixture and the like.In general, the time is 10 to 40 hours.

The polymerization reaction produces poly(3,4-dialkoxythiophene). Thispolymerisation is conducted in presence of a polyanion and thepoly(3,4-dialkoxythiophene), consequently, is complexed with thispolyanion, so that it is referred to as “a complex ofpoly(3,4-dialkoxythiophene) and a polyanion” or simply “a complex” inthis specification.

The coating composition of the present invention can contain a compoundselected from the group of a water-soluble compound having an amidegroup, a water-soluble compound having a hydroxyl group, a water-solublesulfoxide, and a water-soluble sulfone, in addition to the waterdispersion containing the complex of poly(3,4-dialkoxythiophene) and apolyanion. The compound(s) is/are contained in order to improve theconductivity of the coated film.

Examples of the water-soluble compound having an amide group containedin the coating composition of the present invention include, but are notlimited to, N-methyl-2-pyrrolidone, 2-pyrrolidone,N-vinyl-2-pyrrolidone, N-methylformamide, N,N-dimethylformamide, andformamide. Lactones such as γ-butyrolactone have substantially the sameeffects as those of the water-soluble compound having an amide group.Among these, N-methyl-2-pyrrolidone, 2-pyrrolidone,N-vinyl-2-pyrrolidone, N-methylformamide, formamide andN,N-dimethylformamide are preferable. The most preferable compound isN-methylformamide. These amide compounds can be used alone or incombination of two or more.

Preferable examples of the water-soluble compound having a hydroxylgroup contained in the coating composition of the present inventioninclude polyhydric alcohols such as glycerol, 1,3-butanediol, ethyleneglycol, and diethylene glycol monoethylether. They can be used alone orin combination of two or more.

Examples of the water-soluble sulfoxide contained in the coatingcomposition of the present invention include dimethyl sulfoxide anddiethyl sulfoxide.

Examples of the water-soluble sulfone contained in the coatingcomposition of the present invention include diethyl sulfone andtetramethylene sulfone.

For the purpose of improving the film-forming properties and theadhesiveness with the substrate, the coating composition of the presentinvention may contain a water-soluble or water-dispersible binder resin.Examples of the water-soluble or water-dispersible binder resin include,but are not limited to, polyesters, poly(meth)acrylates, polyurethanes,polyvinyl acetate, polyvinylidene chloride, polyamides, polyimides,copolymers having a copolymer component selected from styrene,vinylidene chloride, vinyl chloride, and an alkyl (meth)acrylate.

For the purpose of improving the wettability with the substrate, thecoating composition of the present invention may contain a small amountof a surfactant. Preferable examples of the surfactant include, but arenot limited to, nonionic surfactants (e.g., polyoxyethylene alkyl phenylethers, polyoxyethylene alkyl ethers, sorbitan fatty acid esters, anfatty acid alkylol amides), and fluorocarbon surfactants (e.g.,fluoroalkyl carboxylic acids, perfluoroalkyl benzene sulfonic acids,perfluoroalkyl quarternary ammonium salts, and perfluoroalkylpolyoxyethylene ethanol).

Furthermore, for the purpose of improving the wettability with thesubstrate and the drying properties of the coated film, the coatingcomposition of the present invention may contain water or awater-miscible solvent. Examples of the water-miscible solvent include,but are not limited to, methanol, ethanol, 2-propanol, n-propyl alcohol,isobutanol, ethylene glycol, propylene glycol, acetone, methyl ethylketone, acetonitrile, tetrahydrofuran, dioxane, and a mixed solvent ofthese substances.

Examples of the substrate that is coated with the coating composition ofthe present invention include a plastic sheet, a plastic film, nonwovenfabric, and a glass plate. Examples of plastics that form the plasticsheet or film include polyesters, polystyrene, polyimides, polyamides,polysulfones, polycarbonates, polyvinyl chloride, polyethylene,polypropylene, a blend of these polymers, a copolymer containing amonomer constituting these polymers, a phenol resin, an epoxy resin, andABS resin.

Examples of an appropriate coating process include, but are not limitedto, coating techniques such as gravure coating, roll coating, and barcoating; printing techniques such as screen printing, gravure printing,flexography, offset printing, and ink jet printing; spray coating; anddip coating.

A film (i.e., a conductive transparent film) is formed on a surface of asubstrate by applying to coating composition to the substrate and dryingthe substrate. The coated liquid is dried at 20 to 250° C. for 3 secondsto one week, preferably at 70 to 130° C. for 5 seconds to 60 seconds.

Thus, a coated substrate having the conductive transparent film of thepresent invention can be obtained. The obtained thin film on the surfaceof the substrate has flexibility and remarkably improved transparencyand conductivity, compared with a conventional thin film made of apolythiophene conductive polymer.

The conductive transparent film can be used preferably in surfaceelectrodes of an electroluminescence panel, pixel electrodes of liquidcrystal displays, electrodes of capacitors, various transparentelectrodes such as transparent electrodes of a touch panel, andelectromagnetic shielding of cathode-ray tube displays.

EXAMPLES

Hereinafter, the present invention will be described more specificallyby way of examples and comparative examples. However, the presentinvention is not limited to the examples. It should be noted that theterm “parts” in the following examples and comparative examples refersto “Parts by weight”.

1. Material Used

In the examples and the comparative examples, VERSA-TL 72 (numberaverage molecular weight: 75 000, solid content: 20%) manufactured byNippon NSC Ltd. was diluted, and used as an aqueous solution ofpolystyrene sulfonic acid for producing an aqueous dispersion containinga complex of poly(3,4-dialkoxythiophene) and a polyanion.

For an ion exchange treatment of the water dispersion ofpoly(3,4-dialkoxythiophene) and a polyanion, Lewatit S100H manufacturedby BAYER AG was used as a cation exchange resin, and Lewatit MP62 byBAYER AG was used as an anion exchange resin.

As a polyester resin water dispersion serving as a binder component ofthe coating composition in the examples and the comparative examples,Gabsen ES-210 (solid content: 25%) manufactured by Nagase ChemtexCorporation was used. As the fluorocarbon surfactant, Pluscoat RY-2(solid content: 10%) manufactured by Goo Chemical Co., Ltd. was used.

2. Coating and Drying Process

The coating composition was coated on a substrate and dried in thefollowing manner in the examples and the comparative examples. As thesubstrate, a PET film (Lumirror T-60 manufactured by Toray Industries.Inc.) was used, and the coating composition was applied with a wire bar[No. 8 (for preparing a layer having a thickness of 18.3 μm in a wetcondition), No. 12 (for preparing a layer having a thickness of 27.4 μmin a wet condition, or No. 16 (for preparing a layer having a thicknessof 36.6 μm in a wet condition)], and dried by blowing at 100° C. for 1to 3 minutes, and thus a coated substrate having a thin film wasobtained.

3. Evaluation of the Thin Film on the Surface of the Substrate in theExamples and the Comparative Examples

3.1 The surface resistivity was measured with Loresta-GP (MCP-T600)manufactured by Mitsubishi Chemical Corporation according to JIS K 6911.

3.2 The total light transmission and the haze value were measured with ahaze computer HGM-2B manufactured SUGA Test Instruments Co. Ltd.according to JIS K7150. The total light transmission of an untreated PETfilm (Lumirror T type: Toray) is 87.8%, and the haze value is 1.9%.

3.3 The adhesion of the coated film to the substrate was measuredaccording to the lattice pattern cutting test of JIS K5400.

Example 1

First, 49 parts of a 1% iron (III) sulfate aqueous solution, 8.8 partsof 3,4-ethylenedioxythiophene and 117 parts of a 10.9% peroxodisulfuricacid aqueous solution were added to 1887 parts of an aqueous solutioncontaining 20.8 parts of polystyrene sulfonic acid. The pH of thereaction mixture at this time was 1.34. This reaction mixture wasstirred at 18° C. for 23 hours. Then, 154 parts of cation exchange resinand 232 parts of anion exchange resin were added to the reaction mixtureand stirred for 2 hours. Thereafter, the ion exchange resin was filteredoff so that a deionized water dispersion (2041 parts: solid content of1.32%) containing a complex of poly(3,4-ethylenedioxythiophene) and apolystyrene sulfonic acid was obtained.

Comparative Example 1

First, 49 parts of a 1% iron (III) sulfate aqueous solution, 8.8 partsof 3,4-ethylenedioxythiophene and 17.4 parts of sodium peroxodisulfatewere added to 2012 parts of an aqueous solution containing 22.2 parts ofpolystyrene sulfonic acid. The pH of the reaction mixture at this timewas 1.52. This reaction mixture was stirred at 18° C. for 23 hours.Then, 154 parts of cation exchange resin and 232 parts of anion exchangeresin were added to the reaction mixture and stirred for 2 hours.Thereafter, the ion exchange resin was filtered off so that a deionizedwater dispersion (2066 parts: solid content of 1.37%) containing acomplex of poly(3,4-ethylenedioxythiophene) and a polystyrene sulfonicacid was obtained.

Example 2

First, 49 parts of a 1% iron (III) sulfate aqueous solution, 64.2 partsof a 25% sulfuric acid aqueous solution, 8.8 parts of3,4-ethylenedioxythiophene and 17.4 parts of sodium peroxodisulfate wereadded to 1964 parts of an aqueous solution containing 22.2 parts ofpolystyrene sulfonic acid. The pH of the reaction mixture at this timewas 0.93. This reaction mixture was stirred at 18° C. for 23 hours.Then, 154 parts of cation exchange resin and 232 parts of anion exchangeresin were added to the reaction mixture and stirred for 2 hours.Thereafter, the ion exchange resin was filtered off so that a deionizedwater dispersion (2082 parts: solid content of 1.35%) containing acomplex of poly(3,4-ethylenedioxythiophene) and a polystyrene sulfonicacid was obtained.

Example 3

First, 49 parts of a 1% iron (III) sulfate aqueous solution, 64.2 partsof a 25% sulfuric acid aqueous solution, 8.8 parts of3,4-ethylenedioxythiophene and 120.7 parts of a 10.9% peroxodisulfuricacid aqueous solution were added to 1859 parts of an aqueous solutioncontaining 22.2 parts of polystyrene sulfonic acid. The pH of thereaction mixture at this time was 0.93. This reaction mixture wasstirred at 18° C. for 23 hours. Then, 154 parts of cation exchange resinand 232 parts of anion exchange resin were added to the reaction mixtureand stirred for 2 hours. Thereafter, the ion exchange resin was filteredoff so that a deionized water dispersion (2081 parts: solid content of1.35%) containing a complex of poly(3,4-ethylenedioxythiophene) and apolystyrene sulfonic acid was obtained.

Example 4

First, 49 parts of a 1% iron (III) sulfate aqueous solution, 30 parts ofa concentrated nitric acid solution, 8.8 parts of3,4-ethylenedioxythiophene and 121 parts of a 10.9% peroxodisulfuricacid aqueous solution were added to 1887 parts of an aqueous solutioncontaining 22.2 parts of polystyrene sulfonic acid. The pH of thereaction mixture at this time was 0.83. This reaction mixture wasstirred at 18° C. for 19 hours. Then, 154 parts of cation exchange resinand 232 parts of anion exchange resin were added to the reaction mixtureand stirred for 2 hours. Thereafter, the ion exchange resin was filteredoff so that a deionized water dispersion (2075 parts: solid content of1.36%) containing a complex of poly(3,4-ethylenedioxythiophene) and apolystyrene sulfonic acid was obtained.

Example 5

First, 49 parts of a 1% iron (D) sulfate aqueous solution, 25 parts oftrifluoromethane sulfuric acid, 8.8 parts of 3,4-ethylenedioxythiopheneand 121 parts of a 10.9% peroxodisulfuric acid aqueous solution wereadded to 1850 parts of an aqueous solution containing 22.2 parts ofpolystyrene sulfonic acid. The pH of the reaction mixture at this timewas 1.22. This reaction mixture was stirred at 18° C. for 23 hours.Then, 154 parts of cation exchange resin and 232 parts of anion exchangeresin were added to the reaction mixture and stirred for 2 hours.Thereafter, the ion exchange resin was filtered off so that a deionizedwater dispersion (2033 parts: solid content of 1.39%) containing acomplex of poly(3,4-ethylenedioxythiophene) and a polystyrene sulfonicacid was obtained.

Example 6

First, 49 parts of a 1% iron (III) sulfate aqueous solution, 20 parts ofa concentrated hydrochloric acid solution, 8.8 parts of3,4-ethylenedioxythiophene and 117 parts of a 10.9% peroxodisulfuricacid aqueous solution were added to 1887 parts of an aqueous solutioncontaining 22.2 parts of polystyrene sulfonic acid. The pH of thereaction mixture at this time was 0.95. This reaction mixture wasstirred at 18° C. for 23 hours. Then, 154 parts of cation exchange resinand 232 parts of anion exchange resin were added to the reaction mixtureand stirred for 2 hours. Thereafter, the ion exchange resin was filteredoff so that a deionized water dispersion (2061 parts: solid content of1.37%) containing a complex of poly(3,4-ethylenedioxythiophene) and apolystyrene sulfonic acid was obtained.

Example 7

First, 5 parts of a polyester resin water dispersion, 4 parts ofN-methylformamide and 1 part of a fluorocarbon surfactant were added to90 Parts of the water dispersion containing a complex ofpoly(3,4-ethylenedioxythiophene) and a polystyrene sulfonic acidobtained in Example 1, and the mixture was stirred for one hour, so that100 parts of a coating composition was obtained.

Examples 8 to 12

The same operation as in Example 7 was performed except that the waterdispersion obtained in Example 1 was replaced by each of the waterdispersions obtained in Examples 2 to 6, so that 100 parts of a coatingcomposition were correspondingly obtained.

Comparative Example 2

The same operation as in Example 7 was performed except that the waterdispersion obtained in Example 1 was replaced by the water dispersionobtained in Comparative Example 1, so that 100 parts of a coatingcomposition were obtained.

Example 13

The coating composition obtained in Example 7 was coated onto a surfaceof a PET film with each of the three types of wire bars, and then dried,so that a substrate coated with a thin film was obtained. Table 1 showsthe evaluation results of the total light transmission and the hazevalue of the obtained coated substrate and the surface resistivity andthe adhesion of the thin film on the substrate. The total lighttransmission and the haze value of the PET film used as the substratewere 87.8% and 1.9%.

Examples 14 to 18

The same operation as in Example 13 was performed except that thecoating composition obtained in Example 7 was replaced by each of thecoating compositions obtained in Examples 8 to 12. Table 1 collectivelyshows the evaluation results of the obtained thin films on the surfacesof the substrates.

Comparative Examples 3

The same operation as in Example 13 was performed except that thecoating composition obtained in Example 7 was replaced by each of thecoating compositions obtained in Comparative Examples 2. Table 1collectively shows the evaluation results of the obtained thin films onthe surfaces of the substrates.

TABLE 1 Thin film thickness Total light Surface after dryingtransmission resistivity Haze value Adhesion Wire bar (μm) (%) (Ω/□) (%)(points) Example No. 8 0.33 83.3 9.2E+02 2.1 10 13 No. 12 0.49 79.15.2E+02 2.3 10 No. 16 0.66 75.1 3.5E+02 2.7 10 Example No. 8 0.33 82.28.0E+02 2.3 10 14 No. 12 0.49 77.3 3.8E+02 2.5 10 No. 16 0.66 73.02.7E+02 2.6 10 Example No. 8 0.33 82.7 7.1E+02 2.3 10 15 No. 12 0.4978.0 3.5E+02 2.4 10 No. 16 0.66 74.5 2.6E+02 2.6 10 Example No. 8 0.3381.6 4.5E+02 3.1 10 16 No. 12 0.49 73.9 2.3E+02 3.7 10 No. 16 0.66 72.12.0E+02 3.9 10 Example No. 8 0.33 82.0 5.1E+02 2.8 10 17 No. 12 0.4974.4 2.7E+02 3.5 10 No. 16 0.66 72.2 2.3E+02 3.7 10 Example No. 8 0.3382.4 4.5E+02 2.7 10 18 No. 12 0.49 75.3 2.2E+02 3.2 10 No. 16 0.66 73.02.0E+02 3.3 10 Com. Ex. 3 No. 8 0.33 81.1 1.5E+03 2.8 10 No. 12 0.4975.7 7.0E+02 2.2 10 No. 16 0.66 71.4 5.0E+02 2.5 10

As seen from Table 1, all the examples exhibit higher total lighttransmissions and lower surface resistivities than those of thecomparative example. The haze value and the adhesion in the examples andthose in the comparative examples are substantially equal to each other.Furthermore, the substrates coated with the thin films obtained inExamples 13 to 18 and Comparative Example 3 were bent 50 times each inthe opposite directions so that the radius of the concave portion ofeach of the bent films was 1 cm, and the surface resistivity before andafter the bending was measured. The surface resistivity was notsubstantially changed (within ±5%) in all the cases, which indicatesthat they were flexible. FIG. 1 shows the relationship between the totallight transmission and the surface resistivity of the coated substrateshown in Table 1. The surface resistivity at a total light transmissionof 80% was read, and Table 2 shows the results collectively.

TABLE 2 Surface resistivity Water at total light dispersion transmissionof of complex Oxidizing agent Acid 80% (Ω/□) Example 13 Example 1Peroxodisulfuric acid — 600 Example 14 Example 2 Sodium peroxodisulfateSulfuric acid 560 Example 15 Example 3 Peroxodisulfuric acid Sulfuricacid 470 Example 16 Example 4 Peroxodisulfuric acid conc. Nitric acid390 Example 17 Example 5 Peroxodisulfuric acid Trifluoromethan 420sulfonic acid Example 18 Example 6 Peroxodisulfuric acid conc. 350Hydrochloric acid Com. Ex. 3 Com. Ex. 1 Sodium peroxodisulfate — 1300

As seen from Table 2, in Example 13 where the composition (Example 7)containing the water dispersion (Example 1) produced by usingperoxodisulfuric acid as an oxidizing agent was applied, the surfaceresistivity (600Ω/□) at a total light transmission of 80% was more than50% lower than that of Comparative Example 3 where sodium peroxosulfatewas used.

Also in the case (Example 14) where a composition (obtained in Example8) containing the water dispersion (obtained in Example 2; thisdispersion corresponds to a dispersion that is obtained by addingsulfuric acid to the reaction mixture of Comparative Example 1 to adjustthe pH to be 0.93) was applied, the surface resistivity at a total lighttransmission of 80% was reduced from 1300Ω/□ (Comparative Example 3 thatemploys the dispersion of Comparative Example 1) to 560 Ω/□.

Furthermore, the surface resistivity at a total light transmission of80% was reduced further by using peroxodisulfuric acid as the oxidizingagent, and further adding an organic acid or an inorganic acid to lowerthe pH in the same manner as in Examples 3 to 6 (see Examples 15 to 18).

Thus, a coated substrate having good transparency and conductivity canbe obtained by using peroxodisulfuric acid as an oxidizing agent orusing an arbitrary oxidizing agent in combination with an acid that isused for lowering the pH.

The coating composition containing an aqueous dispersion comprising acomplex of poly(3,4-dialkoxythiophene) and a polyanion of the presentinvention can be easily formed into a film by a wet process, and thisfilm has flexibility and excellent transparency and conductivity.Therefore, the coating composition of the present invention is usefulfor producing surface electrodes of electroluminescence panels, pixelelectrodes of liquid crystal displays, electrodes of capacitors, varioustransparent electrodes such as transparent electrodes of touch panels,and electromagnetic shielding of cathode-ray tube displays. Furthermore,the composition can be formed into a film at a low temperature, and thefilm has flexibility, so that the film is particularly useful as aconductive transparent film formed on a plastic film substrate.

The invention claimed is:
 1. A method for producing an aqueousdispersion containing a complex of a poly(3,4-alkylenedioxythiophene)and a polyanion, comprising:-polymerizing a 3,4-alkylenedioxythiophenerepresented by formula (1):

wherein R¹ and R² together form a C₁₋₄-alkylene group which isoptionally substituted, wherein the polymerization is performed in thepresence of the polyanion by using peroxodisulfuric acid as an oxidizingagent in an aqueous solvent and wherein the pH during polymerization is1.5 or less and wherein said aqueous solvent is water and said polyanionis a polystyrene sulfonic acid and wherein a dried film of thedispersion with film thickness of 0.33 μm has a surface resistivity of150 ohm/square to 920 ohm/square.
 2. The method as claimed in claim 1,wherein R¹ and R² together form a 1,2- ethylene.
 3. The method asclaimed in claim 1, wherein R¹ and R² together form a 1,2- alkylene. 4.The method as claimed in claim 1, wherein R¹ and R² together form a 1,3-alkylene.
 5. The method as claimed in claim 1, wherein R¹ and R²together form a 1,3- propylene.
 6. The method as claimed in claim 1,wherein R¹ and R² together form a methylene.
 7. The method as claimed inclaim 1, wherein the pH during polymerization is 1.0 or less.